Cross Hole Sonic Logging Test

   Cross hole sonic logging is a method to verify the structural integrity of drilled shaft and other concrete piles. This method is covered under ASTM D6760. The method is considered to be more accurate than sonic echo testing in the determination of structural soundness of concrete within the drilled shaft inside of the rebar cage. This method provides little indication of concrete soundness outside the cage.

   Cross Hole Acoustical Testing normally requires steel (preferred) or PVC access tubes installed in the drilled shaft and tied to the rebar cage. Before the rebar cage is placed in the hole, the access tubes are attached to the interior of the rebar cage. The cage is then lowered into the hole and the concrete is placed. Steel tubes are preferred over PVC tubes because studies have shown that PVC tubes tend to de-bond from the concrete due to the heat of hydration process of concrete.

   The tubes are filled with water as an intermediate medium. After curing for 7-14 days, a sound source and receiver are lowered, maintaining a consistent elevation between source and sensor. A signal generator generates a sonic pulse from the emitter which is recorded by the sensor. Relative energy, waveform and differential time are recorded, and logged. This procedure is repeated at regular intervals throughout the pile and then mapped. By comparing the graphs from the various combinations of access tubes, a qualitative idea of the structural soundness of the concrete throughout the pile can be gleaned.